Power module

ABSTRACT

In a powder module ( 111 ), a free-wheeling diode ( 1 A), an IGBH ( 1 B), and a capacitor ( 20 ) for smoothing direct current are disposed directly on a surface ( 2 BS) of a conductive heat sink ( 2 B) with through holes ( 2 BH). The rear electrodes of the free-wheeling diode ( 1 A), the IGBT ( 1 B), and the capacitor ( 20 ) are bonded to the heat sink ( 2 B) for example with solder, whereby the diode ( 1 A), the IGBT ( 1 B), and the capacitor ( 20 ) are electrically connected with the heat sink ( 2 B). The front electrodes of the diodes ( 1 A), the IGBT ( 1 B), and the capacitor ( 20 ) are connected with each other for example by wires ( 7 ). In the heat sink ( 2 B), a cooling medium flows through the through holes ( 2 BH). Such a configuration allows miniaturization of the power module and improves the cooling performance and reliability of the power module.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to power modules and especially totechniques for improving cooling performance of power modules.

2. Description of the Background Art

FIG. 34 is a schematic external view of a first conventional powermodule 101P. In the power module 101P, a copper base plate 9P isdisposed through a heat-conducting grease (not shown) over a radiatingfin or heat sink 2AP, and an insulating substrate 5P is disposed on thebase plate 9P. On the insulating substrate 5P, there are disposed afree-wheeling diode 1AP (hereinafter also referred to as “diode”) and aninsulated gate bipolar transistor 1BP (hereinafter referred to as“IGBT”).

In the conventional power module 101P, copper foils 6P are placed onboth main surfaces of the insulating substrate 5P. The base plate 9P andthe copper foil 6P are bonded together with solder, and the diode 1APand the IGBT 1BT are soldered onto the copper foil 6P. An electrode 3Pis provided through an insulating layer 4P over the radiating fin 2AP.Then, predetermined electrical connections are made by wires 7P. Theconstruction including the radiating fin 2AP, the diode 1AP, the IGBT1BP, and the like is housed in a case (not shown).

The electrode 3P is connected to a bus bar or wiring 91P which extendstoward the outside of the case. Outside the case, a current transformer92P for current detection is attached to the bus bar 91P. Further, acylindrical capacitor 8P for smoothing direct current is providedoutside the case independently of the radiating fin 2P and the like (theconnection with the case is omitted in the figure).

FIG. 35 is a schematic external view of a second conventional powermodule 102P. The power module 102P has no base plate 9P as abovedescribed, wherein the insulating substrate 5P is disposed through aheat-conducting grease over the radiating fin 2AP. The power module 102Pis in all other aspects identical to the above-mentioned power module101P.

FIG. 36 is a schematic external view of a third conventional powermodule 103P. The power module 103P is a so-called power transducer. Inthe power module 103P, all the diodes 1AP and IGBTs 1BP are disposed onthe insulating substrates 5P. A heat sink 2BP of the power module 103Phas through holes 2BHP therethrough passing a cooling medium. The powermodule 103P is in all other aspects identical to the above-mentionedpower module 101P.

The conventional power modules 101P, 102P, and 103P have the followingproblems.

First is low temperature reliability during operation. Morespecifically, when the thermal expansion coefficient of the heat sink2AP or 2BP differs from those of the diode(s) 1AP and the IGBT(s) 1BP,thermal stresses responsive to a temperature difference from thefreezing point of solder will occur at the solder joints as abovedescribed. There is thus a problem of occurrence and progress ofcracking at the solder joints through a heat cycle (or temperaturecycle) in the use (or operation) of the power module 101P, 102P, 103Pand/or a heat cycle by repetitions of start and halt of the powermodule. Such cracking at the solder joints reduces the longevity of thepower module.

To reduce the above thermal stresses, it is contemplated for example toincrease solder thickness (e.g., 300 μm or more). However, suchincreased thickness of solder increases thermal resistance between theheat sink 2AP or 2BP and the diode(s) 1AP and the like. This brings upanother problem that the size of the heat sink 2AP or 2BP must beincreased.

Further, in the conventional power modules 101P, 102P, and 103P, thedistribution of temperature in the insulating substrate(s) 5P, the baseplate 9P, and the like due to heat generation in the diode(s) 1AP andthe like causes warps or winding in the insulating substrate(s) 5P andthe like. When the temperature difference is great, clearance is createdbetween the radiating fin 2AP, 2BP and the base plate 9P and the like.Thus, there is a problem of reduced heat transfer because theheat-conducting grease cannot completely fill in the space between theradiating fin 2AP, 2BP and the insulating substrate(s) 5P or the baseplate 9P (due to the incoming air). Another problem is that theoccurrence or progress of cracking at the solder joints, describedabove, may be encouraged. The formation of clearance thus results indeterioration in the reliability of the power module.

To prevent the formation of clearance, it is contemplated for example tomake the temperature distribution uniform throughout the insulatingsubstrate(s) 5P and the like, or to increase the rigidity of theinsulating substrate(s) 5P and the like by increasing the thickness ofthe substrate(s) 5P and the like. However, such increased thicknessincreases thermal resistance between the heat sink 2AP, 2BP and theinsulating substrate(s) 5P or the like. This brings up, as has beendescribed, another problem that the size of the heat sink 2AP, 2BP mustbe increased.

Further, when the diode(s) 1AP and the IGBT(s) 1BP produce a largequantity of heat, the amount of current must be limited in order toensure reliability since the characteristics of the elements vary withincreasing temperature.

Secondly, each of the conventional power modules 101P, 102P, and 103P asa whole is large in size since the current transformer 92P and thecylindrical capacitor 8P are provided independently outside the case forsuch a module. Besides, the current transformer 92P has the property ofbecoming large when current to be measured has a large DC component, andalso the current transformer 92P makes measurements with errors (about5%) due to its characteristics changes caused by heat generation.

Thirdly, in the power module 103P, the distances from each of the powersemiconductor devices, such as the diode 1AP or the IGBT 1BP, to theelectrode 61P connected to the low potential side of the powertransducer and to the electrode 62P connected to the high potential sidevary according to where that power semiconductor device is located. Thiscauses variations in the inductance of the wiring or wires 7P from onepower semiconductor device to another, thereby causing variations inoutput voltage.

SUMMARY OF THE INVENTION

A first aspect of the present invention is directed to a power modulecomprising: a heat sink; a first power semiconductor device disposeddirectly on the heat sink; and a capacitor disposed directly on the heatsink.

According to a second aspect of the present invention, in the powermodule of the first aspect, the heat sink has a plurality of surfaces;and the first power semiconductor device and the capacitor are disposedon different ones of the surfaces of the heat sink.

According to a third aspect of the present invention, in the powermodule of the first or second aspect, the heat sink has a passage of acooling medium.

According to a fourth aspect of the present invention, in the powermodule of either of the first through third aspects, the heat sink hasconductivity; and an electrode of the first power semiconductor deviceand an electrode of the capacitor are directly bonded to the heat sink.

According to a fifth aspect of the present invention, the power moduleof the fourth aspect further comprises: an insulating substrate disposedon the heat sink; and a second power semiconductor device disposedthrough the insulating substrate over the heat sink.

According to a sixth aspect of the present invention, the power moduleof the fourth aspect further comprises: another heat sink; and a secondpower semiconductor device disposed directly on the another heat sink.

According to a seventh aspect of the present invention, in the powermodule of the sixth aspect, the another heat sink has conductivity; andan electrode of the second power semiconductor device is directly bondedto the another heat sink. The power module further comprises: aninsulating member for insulating the another heat sink from the heatsink and the electrode of the capacitor.

According to an eighth aspect of the present invention, the power moduleof the seventh aspect further comprises: a conductive member disposed onthe insulating member; and a flexible wire connected to the conductivemember for providing an electrical connection between the first powersemiconductor device and the second power semiconductor device.

A ninth aspect of the present invention is directed to a power modulecomprising: a capacitor; and a first semiconductor device disposeddirectly on an electrode of the capacitor.

According to a tenth aspect of the present invention, in the powermodule of the ninth aspect, the electrode of the capacitor has a passageof a cooling medium.

According to an eleventh aspect of the present invention, the powermodule of the ninth aspect further comprises: an insulating substratedisposed on the electrode of the capacitor; and a second powersemiconductor device disposed through the insulating substrate over theelectrode of the capacitor.

According to a twelfth aspect of the present invention, in the powermodule of either of the fifth through eighth and eleventh aspects, thefirst power semiconductor device and the second power semiconductordevice are electrically connected with each other; the first powersemiconductor device forms a lower arm of a power transducer; and thesecond power semiconductor device forms an upper arm of the powertransducer.

According to a thirteenth aspect of the present invention, the powermodule of the twelfth aspect further comprises: a plurality of arms ofthe power transducer, including the upper arm and the lower arm; and acoaxial line protruding through a surface on which the first or secondpower semiconductor device is disposed, the coaxial line including afirst electrode for supplying a first voltage to the first powersemiconductor device of each of the lower arms and a second electrodefor supplying a second voltage to the second power semiconductor deviceof each of the upper arms, wherein the plurality of arms are angularlyspaced at regular intervals about the coaxial line.

A fourteenth aspect of the present invention is directed to a powermodule comprising: a plurality of heat sinks each having a passage of acooling medium; a plurality of power semiconductor devices disposed onthe heat sinks; and a casing having space and being capable of housingthe plurality of heat sinks, wherein the plurality of heat sinks arearranged within the space of the casing, leaving a clearancetherebetween, whereby continuous space including the clearance and thepassages is formed within the space of the casing.

According to a fifteenth aspect of the present invention, in the powermodule of the fourteenth aspect, the passages of the heat sinks pass aninsulative cooling medium.

In accordance with the first aspect, both the first power semiconductordevice and the capacitor are directly disposed on the heat sink. Thepower module can thus be made lighter and smaller than conventionalpower modules wherein those components are provided independently.Further, the heat radiating action of the heat sink inhibits not onlyheat generation in the first power semiconductor device but also thetemperature rise in the capacitor. This allows miniaturization of thecapacitor, a reduction in inductance, and an increase in longevity.

Disposing both the first power semiconductor device and the capacitordirectly on the heat sink also reduces the length of wiring between bothof them shorter than that in the aforementioned conventional powermodules. Thus, circuit inductance can be reduced. This reduces overshootvoltage at a switching operation of the first power semiconductordevice, resulting in a reduction in withstand voltage and loss of thefirst power semiconductor device. The above short wiring length alsoreduces the occurrence of electromagnetic noise can be reduced.

Accordingly, a compact, lightweight, and highly reliable power modulecan be provided.

In accordance with the second aspect, the first power semiconductordevice and the capacitor are disposed on different surfaces of the heatsink. This allows a further reduction in the size and weight of thepower module as compared with the case of disposing both of them on thesame surface. Further, less interference occurs between heat radiationin the first power semiconductor device and that in the capacitor, whichimproves heat radiating performance of the power module.

In accordance with the third aspect, passing a cooling medium throughthe passage in the heat sink further improves the cooling capability ofthe heat sink.

In accordance with the fourth aspect, the heat sink having conductivitycan be used as an electrode. This reduces the number of components suchas wires on the heat sink and processes related to the formation of suchcomponents.

Further, the electrodes of both the first power semiconductor device andthe capacitor are directly bonded to the heat sink. That is, the firstpower semiconductor device and the capacitor are electrically connectedwith each other through the heat sink. In this case, the electricalconnection between both the electrodes becomes shorter than in the casewhere both the electrodes are connected by wiring or the like. Aresultant reduction in circuit inductance leads to a considerablereduction in the aforementioned overshoot voltage and the like.

In accordance with the fifth aspect, the second power semiconductordevice is disposed through the insulating substrate over the heat sink.This makes it possible to dispose power semiconductor devices ofdifferent potentials together on a conductive heat sink in the formationof the circuit.

In accordance with the sixth aspect, the power module further comprisesthe second power semiconductor device disposed on another heat sink. Thecombination of the first and second power semiconductor devicessimplifies circuit configuration.

In accordance with the seventh aspect, another conductive heat sink isinsulated from the above-mentioned conductive heat sink and theelectrode of the capacitor by the insulating member. The first andsecond power semiconductor devices can thus be set at differentpotentials without the use of any insulating substrate. This allows areduction in the number of components by the number of insulatingsubstrates. Further, since the construction including the first powersemiconductor device and one heat sink and the construction includingthe second power semiconductor device and another heat sink are broadlyequivalent, the manufacturing cost of the power module as a whole can bereduced. This results in the provision of a low-cost power module.

In accordance with the eighth aspect, when providing an electricalconnection between the first and second power semiconductor devices, theflexible wire uses, as a relay or junction point, the conductive memberdisposed on the insulating member. This inhibits a deflection or theslack of the wire as compared with the case where those powersemiconductor devices are directly connected by the flexible wirewithout the use of the above conductive member. As a result, shortcircuits due to the slack of the wire can be prevented.

In accordance with the ninth aspect, the first power semiconductordevice is disposed directly on the electrode of the capacitor. The powermodule can thus be lighter and smaller than the conventional powermodules wherein both components are provided independently. Further,since the electrode of the capacitor is used as a heat sink, the heatradiating action of the heat sink inhibits not only heat generation inthe first power semiconductor device but also the temperature rise inthe capacitor.

Disposing the first power semiconductor device on the electrode of thecapacitor also makes the electrical connection between both of themconsiderably shorter than that in the aforementioned conventional powermodules. Thus, circuit inductance can be reduced. This reduces overshootvoltage at a switching operation of the first power semiconductordevice, resulting in a reduction in withstand voltage and loss of thefirst power semiconductor device. The above short wiring length alsoreduces the occurrence of electromagnetic noise.

Accordingly, a compact, lightweight, and highly reliable power modulecan be provided.

In accordance with the tenth aspect, passing a cooling medium throughthe passage in the electrode of the capacitor further improves thecooling capability of the power module.

In accordance with the eleventh aspect, the second power semiconductordevice is disposed through the insulating substrate over the electrodeof the capacitor. This makes it possible to dispose power semiconductordevices of different potentials together over the electrode of thecapacitor in the formation of the circuit.

In accordance with the twelfth aspect, a highly reliable powertransducer can be provided.

In accordance with the thirteenth aspect, the plurality of arms of thepower transducer are angularly spaced at regular intervals about thecoaxial line. Thus, the wiring between each arm and the first and secondelectrodes can be installed in a similar manner. This reduces variationsin the output from each arm and variations in the first voltage, therebyoffering considerable resistance to malfunctions.

In accordance with the fourteenth aspect, the plurality of heat sinksform continuous space including clearances and the passages in the heatsinks, within the space of the casing. At this time, the cooling mediumpasses through the passages in the heat sinks faster than when passingthrough the clearances. This improves the cooling capability of the heatsinks. On the other hand, when the cooling medium passes through theclearances, pressure loss is smaller than when the cooling medium passesthrough the passages. Thus, higher cooling performance can be achievedwith smaller pressure loss.

In accordance with the fifteenth aspect, since an insulative coolingmedium passes through the passages of the heat sinks, the powersemiconductor devices can be isolated from each other without the use ofany insulating substrate even if they are directly disposed on theconductive heat sinks. This allows a reduction in the number ofcomponents by the number of insulating substrates. Further, since theconstructions each including the power semiconductor device and the heatsink are broadly equivalent, the manufacturing cost of the power moduleas a whole can be reduced. This results in the provision of a low-costpower module.

The aforementioned power semiconductor devices, which are insulated fromeach other, can be disposed directly on the conductive heat sinks. Thisimproves heat radiating performance of the power module, therebyimproving the reliability of the power module.

It is therefore an object of the present invention to provide a compact,lightweight, and highly reliable power module.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic external view of a power module according to afirst preferred embodiment.

FIG. 2 is a schematic external view of a power module according to asecond preferred embodiment.

FIG. 3 is a schematic external view of a power module according to athird preferred embodiment.

FIG. 4 is a schematic external view of a power module according to afourth preferred embodiment.

FIG. 5 is a schematic external view of a power module as a first exampleof modification in the fourth preferred embodiment.

FIGS. 6 and 7 are schematic external views of a power module as a secondexample of modification in the fourth preferred embodiment.

FIG. 8 is a schematic external view of a power module as a third exampleof modification in the fourth preferred embodiment.

FIG. 9 is a schematic external view of a power module as a fourthexample of modification in the fourth preferred embodiment.

FIGS. 10 and 11 are schematic external views of a power module accordingto a fifth preferred embodiment.

FIG. 12 is a schematic longitudinal sectional view of the power moduleaccording to the fifth preferred embodiment.

FIG. 13 is a schematic diagram of through holes in the power moduleaccording to the fifth preferred embodiment.

FIG. 14 is a schematic external view of a power module according to asixth preferred embodiment.

FIG. 15 is a schematic external view of a power module as a firstexample modification in the sixth preferred embodiment.

FIG. 16 is a schematic external view of a power module as a secondexample of modification in the sixth preferred embodiment.

FIG. 17 is a schematic external view of a power module according to aseventh preferred embodiment.

FIG. 18 is a schematic external view of a power module as a firstexample of modification in the seventh preferred embodiment.

FIG. 19 is a schematic external view of a power module as a secondexample of modification in the seventh preferred embodiment.

FIG. 20 is a schematic external view of a power module according to aneighth preferred embodiment.

FIG. 21 is a schematic external view of a power module as an example ofmodification in the eighth preferred embodiment.

FIGS. 22 and 23 are schematic external views of a power module accordingto a ninth preferred embodiment.

FIG. 24 is a schematic external view of a power module according to atenth preferred embodiment.

FIG. 25 is a schematic longitudinal sectional view of the power moduleaccording to the tenth preferred embodiment.

FIGS. 26 and 27 are schematic external views of a power module as anexample of modification in the tenth preferred embodiment.

FIGS. 28 to 30 are schematic diagrams of a power module according to aneleventh preferred embodiment.

FIG. 31 is a schematic external view of a power module according to atwelfth preferred embodiment.

FIG. 32 is a schematic external view of a power module according to athirteenth preferred embodiment.

FIG. 33 is a schematic external view of a power module as an example ofmodification in the thirteenth preferred embodiment.

FIG. 34 is a schematic external view of a first conventional powermodule.

FIG. 35 is a schematic external view of a second conventional powermodule.

FIG. 36 is a schematic external view of a third conventional powermodule.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Preferred Embodiment

FIG. 1 is a schematic external view of a power module 101 according to afirst preferred embodiment. As shown in FIG. 1, the power module 101comprises a power semiconductor device (e.g., free-wheeling diode orIGBT) 1 formed for example of a silicon (Si) substrate, a heat sink 2A,electrodes 3, insulating layers 4, and wires 7. For the sake ofsimplicity, the details of the power semiconductor device 1 is notillustrated in FIG. 1.

Specifically, the power semiconductor device 1 is disposed in immediateor direct contact with the heat sink 2A. The power semiconductor device1 has main surfaces 1S1 and 1S2 corresponding to the main surfaces ofthe above-mentioned silicon substrate, in each of which an electrode isformed (not shown). One main surface (hereinafter referred to as “rearsurface”) 1S2 or the electrode (hereinafter referred to as “rearelectrode”) formed in the rear surface 1S2 is for example soldered ontoa plane surface 2AS of the heat sink 2A.

Here “disposing the power semiconductor device 1 directly on the heatsink 2A” implies the absence of the insulating substrate 5P and the baseplate 9P as were in the conventional power modules 101P, 102P, and 103P,and this form of “direct disposition” also includes such a configurationthat an adhesive material (e.g., the above solder) is in between thepower semiconductor device 1 and the heat sink 2A for bonding themtogether. Instead of solder, such an adhesive material may be ahigh-thermal-conductivity adhesive, e.g., an epoxy resin containingconductive powder such as aluminum or silver.

The heat sink 2A is made of a material whose thermal expansioncoefficient is approximately equivalent to that of silicon, such asmolybdenum (Mo), an alloy of copper (Cu) and molybdenum (Mo), tungsten(W), a carbon-fiber composite material, or the like. The heat sink 2A(material whose thermal expansion coefficient is approximatelyequivalent to that of silicon) may also be aluminum (Al) containingcarbon (C) or silicon (Si), or the like. The heat sink 2A has a finnedsurface on the side opposite from the surface 2AS.

The insulating layers 4 are disposed on the heat sink 2A and theelectrodes 3 are disposed on the insulating layers 4. That is, theelectrodes 3 are disposed over the heat sink 2A but insulated from theheat sink 2A by the insulating layers 4. The electrodes 3 areelectrically connected by the wires 7 to the electrode (hereinafterreferred to as “front electrode”) formed in the other main surface(hereinafter referred to as “front surface”) 1S1 of the powersemiconductor device 1. Such electrical connections between theelectrodes 3 and the front electrode of the power semiconductor device 1may be established by application of pressure or a conductive adhesive.

The power module 101 achieves the following effects. Since the powersemiconductor device 1 and the heat sink 2A are broadly equivalent inthermal expansion coefficient, the power module 101, unlike theconventional power modules 101P, 102P, and 103P, can greatly inhibit theoccurrence of cracking at the joints (solder joints) between the powersemiconductor device 1 and the heat sink 2A due to the heat cycle.Accordingly, unlike the conventional power modules 101P, 102P, and 103P,the power module 101 does not have to increase solder thickness and canthus reduce thermal resistance between the power semiconductor device 1and the heat sink 2A. This allows the heat sink to be made lighter andsmaller.

Further, the temperature difference between the power semiconductordevice 1 and the heat sink 2A can be reduced since the powersemiconductor device 1 and the heat sink 2A are in direct contact witheach other. Thus, the thermal stress to be imposed, on the adhesivematerial, between the rear surface 1S2 of the power semiconductor device1 and the surface 2AS of the heat sink 2A will be less than in theconventional power modules 101P, 102P, and 103P even if there is atemperature distribution in the rear surface 1S2 and/or in the surface2AS. This improves the reliability of the power semiconductor device,thereby achieving long-term reliability of the power module.

Second Preferred Embodiment

FIG. 2 is a schematic external view of a power module 102 according to asecond preferred embodiment. As shown in FIG. 2, the power module 102comprises a free-wheeling diode 1A and an IGBT 1B, serving in a pair asthe aforementioned power semiconductor device 1; the heat sink 2A; theelectrode 3; the insulating layer 4; and the wires 7. Components similarto those previously described are denoted by the same reference numeralsand they are considered to be supported by the foregoing description.

The free-wheeling diode 1A has a front surface 1AS1 and a rear surface1AS2 corresponding to the aforementioned front and rear surfaces 1S1 and1S2, respectively and also has a front electrode and a rear electrode(not shown). Similarly, the IGBT 1B has a front surface 1BS1 and a rearsurface 1BS2 corresponding to the aforementioned front and rear surfaces1S1 and 1S2, respectively and also has a front electrode and a rearelectrode (not shown)

Specifically, the heat sink 2A of the power module 102 is made of aconductive material such as an alloy of copper and molybdenum as abovedescribed. The diode 1A and the IGBT 1B are disposed directly on theheat sink 2A with their rear surfaces 1AS2 and 1BS2 in face-to-facecontact with the front surface 2AS of the heat sink 2A. Further, thediode 1A and the IGBT 1B are bonded onto the heat sink 2A with aconductive adhesive material such as solder. This provides electricalconnections between the rear electrodes of the diode 1A and the IGBT 1Bthrough solder and the conductive heat sink 2A. On the other hand, thefront electrodes of the diode 1A and the IGBT 1B are electricallyconnected to the electrode 3 by the wires 7, for example.

In this power module 102, the heat sink 2A having conductivity serves asan electrode. This reduces the numbers of electrodes 3 and insulatinglayers 4 and thereby allows the power module to be made lighter andsmaller.

The heat sink 2A of the power module 102 has a protrusion 2AT thatprotrudes through the front surface 2AS, and both the insulating layer 4and the electrode 3 extend over the protrusion 2AT. The protrusion 2ATof the conductive heat sink 2A and the electrode 3 on the protrusion 2ATcan be utilized as a terminal of the power module 102.

The power module 102 is principally applied in such a circuitconfiguration that the rear electrodes of a plurality of powersemiconductor devices are at the same potential. Alternatively, it isalso possible to mount a plurality of power semiconductor devices whoserear electrodes are at different potentials through the formation of aninsulating substrate with conductive layers, such as copper foils(corresponding to the conventional insulating substrate 5P in FIG. 34),between the heat sink 2A and the power semiconductor devices.

Third Preferred Embodiment

FIG. 3 is a schematic external view of a power module 103 according to athird preferred embodiment. The power module 103 has such aconfiguration that the two power modules 102 are coupled togetherthrough an insulating member 10. The insulating member 10 may be anepoxy resin, injection molded plastic, or the like.

In the power module 103, the electrode 3 of each power module 102extends to the other power module 102 and is electrically connected to(e.g., soldered to) the heat sink 2A of the other power module 102 (cf.protrusions 3T).

The power module 103 can easily be produced since its circuitconfiguration is such that the two prepared power modules 102 are merelycombined together. The use of the compact and lightweight power modules102 allows a reduction in the size and weight of the power module 103.Alternatively, three or more power modules 102 may be combined.

The diodes 1A and the heat sinks 2A may directly be connected with eachother by the wires 7 without the electrodes 3 therebetween. Thus, theelectrodes 3 and the like can be eliminated from the power module.

Fourth Preferred Embodiment

FIG. 4 is a schematic external view of a power module 104 according to afourth preferred embodiment. As shown in FIG. 4, the power module 104comprises the free-wheeling diode 1A, the IGBT 1B, a conductive heatsink 2B, the electrode 3, the insulating layer 4, and the wires 7.

The heat sink 2B is made of the same material as the aforementionedconductive heat sink 2A and has a plane surface 2BS corresponding to theabove surface 2AS. On the surface 2BS, there are disposed the diode 1A,the IGBT 1B, and the insulating layer 4.

Specifically, the heat sink 2B of the power module 104 has two throughholes 2BH as passages of a cooling medium. The through holes 2BH arelocated equally away from the surface 2BS; in other words, they arehorizontally aligned as shown in FIG. 4. Each of the through holes 2BHis so configured as to pass under the diode 1A and the IGBT 1B.Alternatively, there may be one or not less than three through holes2BH.

By passing a cooling medium such as gas (e.g., air, sulfur hexafluoride(SF₆), or carbonic acid gas) or liquid (e.g., water or oil) through thethrough holes 2BH, the power module 104 forcefully cools down the heatsink 2B and hence the diode 1A and the IGBT 1B. This considerablyimproves the cooling capability. As a result, the limits on the amountof current, which have been placed in the conventional power modules101P, 102P, and 103P to ensure reliability, can be relaxed or lifted.Also, the heat sink and hence the power module can be made lighter andsmaller.

First Example of Modification in Fourth Preferred Embodiment

FIG. 5 is a schematic external view of a power module 104A as a firstexample of modification in the fourth preferred embodiment. As shown inFIG. 5, the power module 104A comprises the two power modules 104described above. Those power modules 104 are coupled together byconnecting the through holes 2BH in the heat sinks 2B by pipes 2BJ.

(i) When both the heat sinks 2B are set at the same potential; i.e.,when the rear electrodes of the diodes 1A and the like on both the heatsinks 2B are set at the same potential, at least either the pipes 2BJ orthe cooling medium is made of a conductive material or substance (whichis hereinafter referred to as “conductive coupling”). On the other hand,(ii) when the heat sinks 2B are insulated from each other; i.e., whenthe diodes 1A and the like on the heat sinks 2B are insulated from eachother, both the pipes 2BJ and the cooling medium are made of insulatingmaterials or substances (which is hereinafter referred to as “insulativecoupling”).

(iii) When the aforementioned insulating substrate 5P (and the copperfoils 6P) is provided between the heat sinks 2B and the diodes 1A (cf.FIG. 34) in the above case (i) where at least either the pipes 2BJ orthe cooling medium is made of a conductive material or substance, thediodes 1A and the like on the heat sinks 2B can be insulated from eachother as in the above case (ii). Conversely, the aforementioned (i)conductive and (ii) insulative coupling eliminates the need for usingthe insulating substrate 5P and the like.

Alternatively, three or more power modules 104 may be coupled togetherby the pipes 2BJ for the formation of the power module 104A. At thistime, for conductive coupling, a pump (not shown) to pass a coolingmedium is provided for each single group which is formed of a pluralityof power modules 104 of the same potential. For insulative coupling, onthe other hand, only a single pump is provided for the whole powermodule 104A.

Second Example of Modification in Fourth Preferred Embodiment

FIG. 6 is a schematic external view of a power module 104B as a secondexample of modification in the fourth preferred embodiment. In the powermodule 104B, the two through holes 2BH are located differently away fromthe surface 2BS; in other words, the through holes 2BH are verticallyaligned as shown in FIG. 6.

As is the case for the aforementioned power module 104A, the circuitconfiguration may be such that a plurality of power modules 104B arecoupled together by connecting the through holes 2BH by the pipes 2BJ(see FIG. 7). At this time, the upper through holes 2BH are connectedwith each other and the lower through holes 2BH are connected with eachother by the pipes 2BJ. Specifically, the pipes 2BJ are installed suchthat the cooling medium first enters and flows through the upper throughholes 2BH which are closer to the diodes 1A and the IGBTs 1B, and thenmakes a turn, flowing to the lower through holes 2BH. This accommodatesvariations in the temperature of the cooling medium through the heatsinks 2B as compared with those in the above power module 104, therebyimproving uniformity in cooling capability.

Third Example of Modification in Fourth Preferred Embodiment

FIG. 8 is a schematic external view of a power module 104C as a thirdexample of modification in the fourth preferred embodiment. As shown inFIG. 8, the power module 104C comprise the two power modules 104described above. The power modules 104 are located so that theirsurfaces on the side opposite from the surfaces 2BS of the heat sinks 2Bare in contact with each other.

Fourth Example of Modification in Fourth Preferred Embodiment

FIG. 9 is a schematic external view of a power module 104D as a fourthexample of modification in the fourth preferred embodiment. As shown inFIG. 9, the power module 104D comprises the two power modules 104described above. Those power modules 104 are stacked one above the otherthrough supporting members 15. At this time, (i) both the heat sinks 2Bcan be set at the same potential when at least one of the supportingmembers 15 is made of a conductive material such as a metal, and (ii)they can be insulated from each other when all the supporting members 15are made of insulating materials such as resins.

Fifth Preferred Embodiment

FIGS. 10 and 11 are schematic external views (top and side views) of apower module 105 according to a fifth preferred embodiment.Specifically, FIG. 11 is an external view of the power module 105 asviewed from a direction of the arrow A in FIG. 10. For the sake ofsimplicity, part of the components are not illustrated in FIG. 11. FIG.12 is a schematic longitudinal sectional view of the power module 105.

The power module 105 is a so-called three-phase voltage type powertransducer. The power transducer includes both an inverter and aconverter. In each phase of the power transducer, upper and lower arms,forming in a pair a single arm, are connected in series via an outputterminal, and more specifically, the upper arm is connected between thehigh potential side (corresponding to a second voltage) and the outputterminal, and the lower arm is connected (or grounded) between theoutput terminal and the low potential side (corresponding to a firstvoltage). In terms of equivalent circuits, the power transducer is apolyphase bridge circuit; in this case, the module 105 corresponds to athree-phase bridge circuit.

The power module 105 comprises a cylindrical heat sink 2C having opposedcircular main surfaces (surfaces) 2CS1 and 2CS2. The heat sink 2C hasconductivity.

On one main surface 2CS1 of the heat sink 2C, there are disposed threeinsulating substrates 50U, 50V, and 50W formed for example of ceramicplates. Each of the insulating substrates 50U , 50V, and 50W has mainsurfaces, on both of which copper foils or the like are placed, and isbonded onto the main surface 2CS1 with solder, for example. The abovecopper foils which face the heat sink 2C are provided for good adhesionbetween the insulating substrates 50U, 50V, 50W and the heat sink 2C.The copper foils on the other side of the insulating substrates 50U,50V, and 50W, which do not face the heat sink 2C, form electrodes 60U,60V, and 60W, respectively, to be the output terminals of the powertransducer. The electrodes 60U, 60V, and 60W may be made of otherconductive materials than copper foils.

The insulating substrates 50U, 50V, and 50W are about equally spaced ona circumference which is concentric with that of the circular mainsurface 2CS1, i.e., on a circumference about the center of the mainsurface 2CS1. In other words, the insulating substrates 50U, 50V, and50W are angularly spaced at regular intervals (in this case, 120° fromeach other) with respect to the center of the circular main surface 2CS1and they are also equally away from the above center.

Further, three power semiconductor devices, each consisting of one diode1A and one IGBT 1B, are disposed directly on the main surface 2CS1,adjacent to the insulating substrates 50U, 50V, and 50W. Those powersemiconductor devices are about equally spaced on a circumferenceconcentric with that of the circular main surface 2CS1 so that they arelocated between each of the insulating substrates 50U, 50V, and 50W.Specifically, the rear electrodes of such diodes 1A and IGBTs 1B aredirectly bonded onto the main surface 2CS1 with solder, for example. Thefront electrodes of the diodes 1A and the IGBTs 1B, on the other hand,are electrically connected to the electrodes 60U, 60V, and 60W by thewires 7, for example. Disposed directly on the heat sink 2C as abovedescribed, each of the three pairs of diodes 1A and IGBTs 1B forms onelower arm of the power transducer.

On the main surface 2CS1, there are further disposed the insulatingsubstrates 5, which are formed for example of ceramic plates, in closeproximity to the insulating substrates 50U, 50V, and 50W. Thoseinsulating substrates 5 are equally spaced on a circumference concentricwith that of the circular main surface 2CS1 so that they are locatedbetween each of the insulating substrates 50U, 50V, and 50W. Each of theinsulating substrates 5 has main surfaces, on both of which copper foilsor the like are placed, and is boded onto the main surface 2CS1 withsolder, for example. The copper foils which do not face the heat sink 2Cform conductive layers 6.

On each of the conductive layers 6 formed on the insulating substrates5, a diode 1A and an IGBT 1B are disposed. The diode 1A and the IGBT 1Bare bonded together with solder for example so that their rearelectrodes are in face-to-face contact with the conductive layer 6. Theadjacent conductive layer 6 and electrode 60U, 60V, or 60W are connectedby the wires 7, for example. Disposed through the insulating substrate 5over the heat sink 2C, each of the three pairs of diodes 1A and IGBTs 1Bforms one upper arm of the power transducer.

According to such disposition of the diodes 1A and the like, the threearms of the power module 105 (each consisting of the upper and lowerarms) are angularly spaced at regular intervals with respect to thecenter (where an electrode 61 is disposed as will be described later) ofthe circular main surface 2CS1 of the heat sink 2C.

On the circular main surface 2CS1, an insulating substrate 50C formedfor example of a ceramic plate is further disposed around the center ofits circle. The insulating substrate 50C has main surfaces, on both ofwhich copper foils or the like are placed, and is bonded onto the mainsurface 2CS1 with solder, for example. The copper foil which does notface the heat sink 2C forms a conductive layer 60C. The front electrodesof the diode 1A and the IGBT 1B on each of the insulating substrates 5are electrically connected to the conductive layer 60C by the wires 7,for example. The shapes of the insulating substrate 50C, the conductivelayer 60C, and the like are not limited to those illustrated in thefigures.

Specifically, a rod-shaped electrode 61 for example extends out throughthe insulating substrate 50C, from approximately the center of thecircular main surface 2CS1 where the diodes 1A and the like are disposed(see FIG. 12). The electrode 61 is electrically connected to the heatsink 2C. There is further disposed an electrode 62 in electricalconnection with the conductive layer 60C. The electrode 62 is forexample a cylindrical electrode into which the electrode 61 is inserted.The electrodes 61 and 62 are insulated from each other with aninsulating member 11 therebetween. Further, the electrodes 61 and 62form a so-called coaxial line. In the power module 105, the electrode 61is regarded as the “first electrode” and the electrode 62 as the “secondelectrode”.

With such a configuration, the power module 105 forms a power transducerhaving five electrodes 60U, 60V, 60W, 61, and 62.

FIG. 13, corresponding to FIG. 10, is a schematic diagram illustratingthrough holes 2CH in the heat sink 2C. For the sake of simplicity, theinsulating substrates 5 and the like in FIG. 10 are not illustrated inFIG. 13. As shown, the heat sink 2C has three through holes 2CH, each inthe general shape of a ring and concentric with the circumference of themain surface 2CS1 (shown by different broken lines). By passing acooling medium through each of the through holes 2CH, the power module105 is cooled down. The number of through holes 2CH is not limited tothree, but those holes 2CH should preferably be formed under the diodes1A and the IGBT 1B which are heating elements. Alternatively, thethrough holes 2CH may take a spiral form for example, instead of beingshaped like rings. Further, as is the case for the power module 104B(cf. FIG. 6), the through holes 2CH may be aligned vertically betweenthe main surfaces 2CS1 and 2CS2.

According to the power module 105, as have been described, the threearms of the power transducer are about equally spaced on thecircumference concentric with that of the main surface to surround theabove coaxial line. Thus, the wiring between the electrodes 61, 62 andeach arm can be installed in a similar manner. This reduces variationsin the outputs from those arms, and variations in voltage on the lowpotential side, thereby offering considerable resistance tomalfunctions. As a result, a highly reliable power transducer can beprovided.

Example of Modification in Fifth Preferred Embodiment

While in the power module 105, all the diodes 1A and the like aredisposed on the main surface 2CS1 of the heat sink 2C, part of them maybe disposed on the other main surface 2CS2 of the heat sink 2C. Forexample, the three insulating substrates 5 and the components to bedisposed thereon may be disposed on the main surface 2CS2 andpredetermined wiring may be installed therefor.

Sixth Preferred Embodiment

FIG. 14 is a schematic external view of a power module 111 according toa sixth preferred embodiment. In the power module 111 as shown in FIG.14, the diode 1A, the IGBT 1B, and a capacitor 20 for smoothing directcurrent are directly disposed on the surface 2BS of the aforementionedconductive heat sink 2B having the through holes 2BH. The diode 1A andthe IGBT 1B form a “first power semiconductor device”.

As has been described, the diode 1A has main surfaces (front surface1AS1 and rear surface 1AS2) corresponding to the main surfaces of thesilicon substrate, and more specifically, the front surface 1AS1 has afront electrode therein and the rear surface 1AS2 has a rear electrodetherein. Similarly in the IGBT 1B, a front electrode is formed in thefront surface 1BS1 and a rear electrode in the rear surface 1BS2. Forthe sake of simplicity, the details of the front electrodes and the rearelectrodes of the diode 1A and the IGBT 1B are not illustrated in FIG.14.

Unlike the conventional cylindrical capacitor 8P, the capacitor 20 is aplate capacitor with two opposed main surfaces 20S1 and 20S2. One mainsurface (hereinafter referred to as “rear surface”) 20S2 of the platecapacitor has an electrode therein (not shown: hereinafter referred toas “rear electrode”) and the other main surface (hereinafter referred toas “front surface”) 20S1 has another electrode therein (not shown:hereinafter referred to as “front electrode”).

The rear electrodes of the diode 1A, the IGBT 1B, and the capacitor 20are bonded to the heat sink 2B with solder, for example. This provideselectrical connections between each of the rear electrodes through theconductive heat sink 2B. On the other hand, the front electrodes (whichdo not face the heat sink 2B) of the diode 1A, the IGBT 1B, and thecapacitor 20 are connected by the wires 7. Alternatively, electricalconnections may be established between each of the front electrodes byapplication of pressure or a conductive adhesive.

The power module 111 achieves the following effects. First of all, it iscompact in size, lightweight, and highly reliable.

More specifically, since the diode 1A, the IGBT 1B, and the capacitor 20are disposed directly on the heat sink 2B, the power module 111 can bemade smaller than the conventional power modules 101P, 102P, and 103Pwherein those components are provided independently. Further, the heatradiating action of the heat sink 2B inhibits not only heat generationin the diode 1A and the IGBT 1B but also the temperature rise in thecapacitor 20. This allows miniaturization of the capacitor 20, lowerinductance, and an increase in longevity.

Disposing the diode 1A, the IGBT 1B, and the capacitor 20 directly onthe heat sink 2B also reduces the length of wiring between the diode 1Aor the IGBT 1B and the capacitor 20 shorter than in the conventionalpower modules 101P, 102P, and 103P. Especially because the heat sink 2Bhas conductivity, the electrical connections among the diode 1A, theIGBT 1B, and the capacitor 20 can be established by the shortest paththrough the heat sink 2B. The power module 111 can thus have lowercircuit inductance than the conventional power modules 101P, 102P, and103P. This reduces overshoot voltage at a switching operation of thediode 1A and the IGBT 1B, resulting in a reduction in withstand voltageand loss of the diode 1A and the IGBT 1B. Further, the above shortwiring length reduces the occurrence of electromagnetic noise.

According to the power module 11, the heat sink 2B having conductivitycan be used as an electrode. This reduces the number of components suchas wires that were necessary for insulative heat sinks and eliminatesprocesses related to the formation of such components.

The cooling capability of the heat sink 2B can be improved by passing acooling medium through the through holes 2BH in the heat sink 2B.

First Example of Modification in Sixth Preferred Embodiment

The aforementioned effects can also be achieved by replacing the heatsink 2B with the conductive heat sink 2A with a fin structure as in apower module 111A in FIG. 15.

Second Example of Modification in Sixth Preferred Embodiment

The capacitor 20, and the diode 1A and the IGBT 1B may be disposed ondifferent surfaces of the heat sink 2B. More specifically, as in a powermodule 111B in FIG. 16, the diode 1A and the IGBT 1B may be disposed onthe surface 2BS of the heat sink 2B and the capacitor 20 may be disposedon another surface (side face) 2BS3 adjacent to the surface 2BS. Or thecapacitor 20 may be disposed on the surface 2BS2 opposed to the surface2BS. Such a configuration is also applicable to the case of using theheat sink 2A.

This power module 111B can be made lighter and smaller than the powermodule 111. Further, less interference occurs between heat radiation inthe diode 1A and the IGBT 1B and that in the capacitor 20, whichimproves heat radiating performance of the power module.

Seventh Preferred Embodiment

FIG. 17 is a schematic external view of a power module 112 according toa seventh preferred embodiment of the present invention. As is evidentfrom the comparison between FIG. 17 and FIG. 14 described earlier, thepower module 112 comprises a capacitor dielectric 33 and a capacitorelectrode 31, instead of the capacitor 20 (cf. FIG. 14). Morespecifically, with the capacitor dielectric 33 sandwiched between theconductive heat sink 2B and the capacitor electrode 31, the heat sink2B, the capacitor dielectric 33, and the capacitor electrode 31constitute a plate capacitor 30 corresponding to the aforementionedcapacitor 20. The power module 112 is in all other aspects identical tothe power module 111.

The capacitor electrode 31 corresponds to the front electrode of thecapacitor 20 and the heat sink 2B to the rear electrode. In this powermodule 112, the diode 1A and the IGBT 1B can be considered to bedisposed on the rear electrode of the capacitor 30.

The power module 112 achieves similar effects to those of theaforementioned power module 111.

First Example of Modification in Seventh Preferred Embodiment

The heat sink 2B may be replaced with the conductive heat sink 2A havinga fin structure as in a power module 112A in FIG. 18.

Second Example of Modification in Seventh Preferred Embodiment

FIG. 19 is a schematic external view of a power module 112B as a secondexample of modification in the seventh preferred embodiment. In thepower module 112B, as is the case for the power module 111B (cf. FIG.16), the capacitor dielectric 33 and the capacitor electrode 31 aredisposed on either the surface 2BS2 or 2BS3 of the heat sink 2B otherthan the surface 2BS. Such a configuration is also applicable to thecase of using the heat sink 2A. The power module 112B achieves similareffects to those of the aforementioned power module 111B.

Eighth Preferred Embodiment

FIG. 20 is a schematic external view of a power module 111C according toan eighth preferred embodiment. This power module 111C is a so-calledthree-phase voltage type power transducer.

In the power module 111C, the capacitor 20 is disposed directly on theheat sink 2B with its rear surface 20S2 in face-to-face contact with thesurface 2BS2 of the heat sink 2B.

The power module 111C comprises three arms for power transducer. Onediode 1A and one IGBT 1B, forming in a pair the lower arm of each arm,are both disposed directly on the surface 2BS of the heat sink 2B withtheir rear electrodes in face-to-face contact with the heat sink 2B. Thefront electrodes of, respectively, the lower-arm diode 1A and IGBT 1Bare electrically connected, for example by the wires 7, to the electrode60U, 60V, or 60W to be the output terminal of the power transducer. Theelectrodes 60U, 60V, and 60W are disposed through the insulatingsubstrates (or insulating layers) 50U, 50V, and 50W, respectively, overthe surface 2BS of the heat sink 2B.

On the other hand, one diode 1A and one IGBT 1B (which form a “secondpower semiconductor device”) forming in a pair the upper arm of each armare disposed through the insulating substrate 5 over the surface 2BS ofthe heat sink 2B. The rear electrodes of the upper-arm diode 1A and IGBT1B are electrically connected to the conductive layer 6 formed on theinsulating substrate 5. The conductive layers 6 are electricallyconnected, for example by the wires 7, to the electrodes 60U, 60V, and60W corresponding to the respective arms. The front electrodes of theupper-arm diode 1A and IGBT 1B are electrically connected, for exampleby the wires 7, to the electrode 61 which is common to all the arms.

The electrode 61 extends from the surface 2BS of the heat sink 2B acrossthe surface 20S1 of the capacitor 20 and is electrically connected tothe front electrode of the capacitor 20. Further, the electrode 61 isisolated from the capacitor 20, excluding the surface electrode, and theheat sink 2B by an insulating layer 50.

In the power module 111C, the electrode 61 is the “second electrode”“connected to the high potential side and the heat sink 2B is the “firstelectrode” connected to the low potential side.

According to the power module 111C, the diodes 1A and the IGBTs 1B ofthe upper arms are disposed through the insulating substrate 5 over theheat sink 2B. Thus, diodes 1A and IGBTs 1B having rear electrodes ofdifferent potentials may be disposed together on the conductive heatsink 2B for the formation of the circuit.

Example of Modification in Eighth Preferred Embodiment

FIG. 21 is a schematic external view of a power module 112C as anexample of modification in the eighth preferred embodiment. Like theaforementioned power module 111C, the power module 112C is a so-calledthree-phase voltage type power transducer.

As is evident from the comparison between FIG. 21 and FIG. 20 describedearlier, the power module 112C comprises the capacitor electrode 31 andthe capacitor dielectric 33 instead of the capacitor 20 in the powermodule 111C. Specifically, the capacitor dielectric 33, which is locatedin face-to-face contact with the surface 2BS2 of the heat sink 2B, issandwiched between the heat sink 2B and the capacitor electrode 31. Withsuch a configuration, the heat sink 2B, the capacitor dielectric 33, andthe capacitor electrode 31 constitute the aforementioned plate capacitor30. The power module 112C is in all other aspects identical to the powermodule 111C.

According to the power module 112C, the diodes 1A and the IGBTs 1B canbe considered to be disposed on one of the electrodes of the capacitor30. Thus, the power module 112C can achieve similar effects to those ofthe power module 112. Further as in the aforementioned power module111C, the presence of the insulating substrates 5 makes it possible todispose diodes 1A and the IGBTs 1B, whose rear electrodes are atdifferent potentials, together on one of the electrodes of the capacitor30.

Ninth Preferred Embodiment

FIGS. 22 and 23 are schematic external views of a power module 113according to a ninth preferred embodiment. FIG. 23 is an external view(side view) of the power module 113 as viewed from a direction of thearrow A in FIG. 22. For the sake of simplicity, the diodes 1A, the IGBTs1B, and the wires 7 are not illustrated in FIG. 23. Like theaforementioned power module 111C, the power module 113 is a so-calledthreephase voltage type power transducer.

In the power module 113, as is evident from the comparison between FIG.22 and FIG. 22 described earlier, the diodes 1A and the IGBTs 1B of allthe lower arms of the power transducer are disposed directly on thesurface 2BS of a single lower-arm heat sink 2B. The lower-arm heat sink2B and the capacitor 20 are provided so that the front surface 2BS2 ofthe lower-arm heat sink 2B and the rear surface 20S2 of the capacitor 20are in face-to-face relationship. The rear electrodes of the lower-armheat sink 2B and the capacitor 20 are thus in electrical contact witheach other.

On the other hand, the diode 1A and the IGBT 1B of each upper arm of thepower transducer are disposed directly on each upper-arm heat sink(another heat sink) 2B having conductivity and are electricallyconnected to the electrode 61 as in the power module 111C (cf. FIG. 20).The three upper-arm heat sinks 2B are coupled but insulated from eachother (the pipes 2BJ are not illustrated in FIG. 22). They are alsoinsulated from the rear electrodes of the lower-arm heat sink 2B and thecapacitor 20 by the insulating member 10. With the insulating member 10,the four heat sinks 2B and the capacitor 20 are integrally coupledtogether.

The upper-arm heat sinks 2B are electrically connected to thecorresponding electrodes 60U, 60V, and 60W by the wires (flexible wires)7, for example. Especially, those wires 7 establish electricalconnections between the upper arms and the lower arms, using, as relayor junction points, the portions (conductive materials) of theelectrodes 60U, 60V, and 60W located above the insulating member 10.

In the power module 113, as has been described, the four heat sinks 2Bare insulated from each other by the insulating member 10. Thus, unlikethe above-mentioned power module 111C (cf. FIG. 20), the power module113 can set the rear electrodes of the upper-arm diodes 1A and IGBTs 1Band those of the lower-arm diodes 1A and IGBTs 1B at differentpotentials without the use of the insulating substrates 5. This allows areduction in the number of components by the number of insulatingsubstrates 5.

In the power module 113, the upper and lower arms are broadly equivalentin construction; therefore, manufacturing cost of the power module as awhole can be reduced. This results in the provision of a low-cost powermodule.

Further, the wires 7 which couple the upper and lower arms together ashave been described, are connected to the portions (conductive members)of the electrodes 60U, 60V, and 60W located above the insulating member10. This inhibits deflection or the slack of those wires as comparedwith the case where the upper and lower arms are directly connected witheach other without passing through the above conductive materials. As aresult, short circuits due to the slack of the wires can be prevented.

Tenth Preferred Embodiment

FIG. 24 is a schematic external view (side view) and FIG. 25 is aschematic longitudinal sectional view of a power module 111D accordingto a tenth preferred embodiment. As is evident from the comparisonbetween FIG. 24 and FIG. 11 described earlier, the power module 111D isbasically configured such that the capacitor 20 is added to theaforementioned power module 105. Since the components identical to thoseof the power module 105 are supported by the foregoing description, thefollowing description concentrates on the features of the power module111D. As in FIG. 11, part of the components are not illustrated in FIG.24.

Each of the three lower arms of the power transducer comprises the diode1A and the IGBT 1B which are disposed directly on the heat sink 2C, andeach of the three upper arms of the power transducer comprises the diodeIA and the IGBT 1B which are disposed through the insulating substrate 5over the heat sink 2C.

In the power module 111D, the capacitor 20 is disposed directly on thecircular main surface 2CS2 of the conductive heat sink 2C. At this time,the rear surface 20S2 of the capacitor 20 is in face-to-face contactwith the heat sink 2C, so there is an electrical connection between arear electrode 20E2 of the capacitor 20 (see FIG. 25) and the heat sink2C.

The power module 111D differs from the aforementioned power module 105in the connection between the electrodes 61 and 62. More specifically,as shown in FIG. 25, the rod-shaped electrode 61 extends through theheat sink 2C and part of the capacitor 20 (other than a surfaceelectrode 20E1) and is electrically connected to the front electrode20E1 of the capacitor 20. At this time, the insulating member 11 alsoextends along with the electrode 61, so that the electrode 61 isinsulated from the heat sink 2C and part of the capacitor 20 (other thanthe surface electrode 20E1). The cylindrical electrode 62, on the otherhand, extends through the insulating substrate 50C and is electricallyconnected to the heat sink 2C.

In the power module 111D, the electrode 61 is the “second electrode”connected to the high potential side of the power transducer, and theelectrode 62 is the “first electrode” connected to the low potentialside.

Like the aforementioned power module 105, the power module 111D can be ahighly reliable power transducer because of the arrangement of the threearms around the coaxial line. Also, it can be made lighter and smallerthan the conventional power module 103P.

Example of Modification in Tenth Preferred Embodiment

FIG. 26 is a schematic external view and FIG. 27 is a schematiclongitudinal sectional view of a power module 112D as an example ofmodification in the tenth preferred embodiment. Like the aforementionedpower module 111D, the power module 112D is a so-called three-phasevoltage type power transducer.

As is evident from the comparison between FIG. 26 and FIG. 24 describedearlier, the power module 112D comprises the capacitor electrode 31 andthe capacitor dielectric 33, instead of the capacitor 20 in the powermodule 111D. More specifically, the capacitor dielectric 33, which islocated in face-to-face contact with the main surface 2CS2 of the heatsink 2C, is sandwiched between the heat sink 2C and the capacitorelectrode 31. Thus, the heat sink 2C, the capacitor dielectric 33, andthe capacitor electrode 31 constitute the aforementioned plate capacitor30. As in the power module 111D, the rod-shaped electrode 61 in thepower module 112D extends through the heat sink 2C and the capacitordielectric 33 and is electrically connected to the capacitor electrode31. The power module 112D is in all other aspects identical to the powermodule 111D, thereby achieving similar effects to those of the powermodule 111D.

In the power module 112D, the diodes 1A and the IGBTs 1B can beconsidered to be located on the rear electrode of the capacitor 30.Thus, the power module 112D can achieve similar effects to those of thepower module 112.

Eleventh Preferred Embodiment

FIGS. 28 through 30 are schematic diagrams of a power module 111Eaccording to an eleventh preferred embodiment. Because the power module111E is based on the aforementioned power module 111D and for the sakeof simplicity, part of the wires 7 are not illustrated in FIG. 28 andthe electrodes 60U, 60V, 60W and the like are not illustrated in FIGS.29 and 30.

While in the aforementioned power module 111D, all the diodes 1A and theIGBTs 1B are disposed on one main surface 2CS1 of the heat sink 2C, thediodes 1A and the IGBTs 1B in the power module 111E are spread over themain surface 2CS1 of the heat sink 2C and the surface 20S1 of thecapacitor 20.

More specifically, the diodes 1A and the IGBTs 1B, forming the lowerarms of the power transducer, are disposed directly on the main surface2CS1 of the heat sink 2C (see FIG. 29). The front electrodes of thediode 1A and the IGBT 1B of each lower arm are connected with eachother. On the other hand, the insulating substrates 5 are disposed onthe surface 20S1 (more correctly the front electrode) of the capacitor20, and the diodes 1A and the IGBTs 1B, forming the upper arms of thepower transducer, are disposed on the conductive layers 6 formed on theinsulating substrates 5 (see FIG. 30). The front electrodes of thediodes 1A and the IGBTs 1B on the insulating substrates 5 are connectedto the surface 20S1 of the capacitor 20.

The conductive layers 6, which have electrical connections with the rearelectrodes of the upper-arm IGBTs 1B, are connected to the frontelectrodes of the lower-arm IGBTs 1B to form the arms of the powertransducer (see the wires 7B). The above junction points at the threearms form the electrodes 60U, 60V, and 60W. Thus, the power module 111Ecan achieve similar effects to those of the power module 111D.

In the power module 111E, the heat sink 2C is connected to the lowpotential side and the front electrode of the capacitor 20 to the highpotential side. Although not illustrated in FIGS. 28 to 30, the coaxialline as in the power module 111D (cf. FIG. 25) may be used for thesupply of power; in such a case, the electrode 62 is the “firstelectrode” and the electrode 61 is the “second electrode”.

Further, as can be seen from the relationship between the power modules111D and 112D, the capacitor 20 in the-power module 111E may be replacedwith the capacitor dielectric 33 and the capacitor electrode 31.

Twelfth Preferred Embodiment

FIG. 31 is a schematic external view of a power module 201 according toa twelfth preferred embodiment. The power module 201 comprises aninsulative casing 202 with two recesses (spaces) 202K. In the casing202, each recess 202K houses a row of alternate heat sinks 2B: ones withthe diode 1A directly disposed thereon and the others with the IGBT 1Bdirectly disposed thereon. The connections between the diodes 1A and theIGBT 1B are not illustrated in FIG. 31.

In each recess 202K, a clearance 203 is created between each of the heatsinks 2B. The orientation of the heat sinks 2B and the through holes 2BHis determined so that the adjacent clearances 203 between the heat sinks2B form contiguous space with the through holes 2BH. Further, the sizesof the heat sinks 2B and the recesses 202K are defined in order not tocreate any other clearance than the clearances 203 between the insidesurfaces of the recesses 202K and the heat sinks 2B.

The clearances 203 are also created at both ends of the alignment of theheat sinks 2B in each recess 202K, and each recess 202K or casing 202has holes connected to those clearances 203. One of such holes of eachrecess 202K is connected to the pipe 2BJ, and the other hole isconnected to the same of the other recess 202K by the pipe 2BJ. Thus,the two recesses 202K are coupled together.

The clearances 203 are covered with an insulative cover (not shown)which is part of the casing 202, so both the recesses 202K formcontinuous space. In the power module 201, therefore, a cooling mediumis poured from the above one of the holes of either of the recesses 202Kthereby to pass the cooling medium through both the recesses 202K Atthis time, since the casing 202 and the above cover are both insulative,the use of an insulative cooling medium for example allows the heatsinks 2B to be insulated from each other (insulative coupling). Examplesof such an insulative cooling medium include gas such as air and sulfurhexafluoride (SF₆), or liquid such as water and oil. Further, the use ofa conductive cooling medium for example allows the conductive heat sinks2B to be at the same potential (conductive coupling). Alternatively,when insulative and conductive heat sinks 2B are combined and aconductive cooling medium is used, conductive coupling of only desiredconductive heat sinks 2B becomes possible.

The diodes 1A and/or the IGBTs 1B may be disposed through the insulatingsubstrates 5 over the heat sinks 2B. In this case, even with the use ofconductive heat sinks 2B, desired diodes 1A and/or the IGBTs 1B can beinsulated from others. Conversely, conductive/insulative properties ofthe heat sinks 2B can eliminate the need of the insulating substrates 5as above described. Alternatively, a plurality of power semiconductordevices may be disposed on a single heat sink 2B.

Since the heat sinks 2B are aligned with the clearance 203 therebetween,the cooling medium passes through alternately the clearances 203 and thethrough holes 2BH narrower than the clearance 203. When passing throughthe through holes 2BH, i.e., when passing under the diodes 1A and theIGBTs 1B as heating elements, the cooling medium flows faster than whenpassing through the clearances 203. This improves cooling effects. Onthe other hand, since the flow of the cooling medium when passingthrough the clearances 203 is slower than when the cooling medium passesthrough the through holes 2BH, pressure loss can be suppressed. Thepower module 201 can thus achieve higher cooling performance withsmaller pressure loss.

As above described, the use of an insulative cooling medium makes itpossible to insulate the power semiconductor devices from each otherwithout the use of the insulating substrates 5, even if the diodes 1Aand/or the IGBTs 1B are disposed directly on the conductive heat sink2B. This allows a reduction in the number of components by the number ofinsulating substrates 5. Also, since the heat sinks 2B with the diode 1Aand/or the IGBT 1B are broadly equivalent in construction, manufacturingcost and price of the power module as a whole can be reduced.

Because each of the above power semiconductor devices are insulated fromeach other, they can be disposed directly on the conductive heat sink2B. This improves heat radiating performance of the power module,resulting in improvements in reliability.

Thirteenth Preferred Embodiment

FIG. 32 is a schematic external view of a power module 114 according toa thirteenth preferred embodiment. As shown in FIG. 32, the power module114 further comprises shunt resistors 90 for measuring current, besidesthe components of the aforementioned power module 113 shown in FIG. 22.More specifically, the shunt registers 90 make direct connections withthe output ends of the electrodes 60U, 60V, and 60W, and each of theshunt register 90 forms the output terminal of the power transducer.

The power module 114 measures current using the shunt registers 90 whichdo not require a control power source and would have no offset inprinciple unlike the current transformer 92P in the conventional powermodules 101P or the like.

Since the shunt registers 90 are directly connected to the output endsof the electrodes 60U, 60V, and 60W, the power module as a whole can bemade lighter and smaller than the conventional power modules 101P or thelike wherein the current transformer 92P is provided independentlyoutside the case. Also, the number of current-measuring components canbe reduced.

Example of Modification in Thirteenth Preferred Embodiment

FIG. 33 is a schematic external view of a power module 114A as anexample of modification in the thirteenth preferred embodiment. As isevident from the comparison between FIG. 33 and FIG. 32 describedearlier, the shunt resistors 90 in the power module 114A are directlyconnected to the electrodes 60U, 60V, and 60W in face-to-facerelationship with the surface 2BS of the heat sink 2B.

In the power module 114A, the temperature rise in the shunt registers 90can be inhibited by the action of the heat sinks 2B. This considerablyprevents changes in the characteristics of the shunt resistors 90 due totemperature variations, resulting in further improvements in accuracy indetecting the amount of current. Further, since the shunt registers 90are located above the heat sinks 2B, the power module 114A can be madelighter and smaller than the aforementioned power module 114.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A power module comprising: a heat sink; a firstpower semiconductor device disposed directly on said heat sink; acapacitor disposed directly on said heat sink; an insulating substratedisposed on said heat sink; and a second power semiconductor devicedisposed through said insulating substrate over said heat sink, whereinsaid heat sink has conductivity and an electrode of said first powersemiconductor device and an electrode of said capacitor are directlybonded to said heat sink.
 2. The power module according to claim 1,wherein said heat sink has a plurality of surfaces; and said first powersemiconductor device and said capacitor are disposed on different onesof said surfaces of said heat sink.
 3. The power module according toclaim 1, wherein said heat sink has a passage of a cooling medium. 4.The power module according to claim 1, further comprising: another heatsink; and a second power semiconductor device disposed directly on saidanother heat sink.
 5. The power module according to claim 4, whereinsaid another heat sink has conductivity; and an electrode of said secondpower semiconductor device is directly bonded to said another heat sink,said power module further comprising: an insulating member forinsulating said another heat sink from said heat sink and said electrodeof said capacitor.
 6. The power module according to claim 5, furthercomprising: a conductive member disposed on said insulating member; anda flexible wire connected to said conductive member for providing anelectrical connection between said first power semiconductor device andsaid second power semiconductor device.
 7. The power module according toclaim 1, wherein said first power semiconductor device and said secondpower semiconductor device are electrically connected with each other;said first power semiconductor device forms a lower arm of a powertransducer; and said second power semiconductor device forms an upperarm of said power transducer.
 8. The power module according to claim 7,further comprising: a plurality of arms of said power transducer,including said upper arm and said lower arm; and a coaxial lineprotruding through a surface on which said first or second powersemiconductor device is disposed, said coaxial line including a firstelectrode for supplying a first voltage to said first powersemiconductor device of each of said lower arms and a second electrodefor supplying a second voltage to said second power semiconductor deviceof each of said upper arms, wherein said plurality of arms are angularlyspaced at regular intervals about said coaxial line.
 9. The power moduleaccording to claim 4, wherein said first power semiconductor device andsaid second power semiconductor device are electrically connected witheach other; said first power semiconductor device forms a lower arm of apower transducer; and said second power semiconductor device forms anupper arm of said power transducer.
 10. The power module comprising: aplurality of heat sinks each having a passage of cooling medium; aplurality of power semiconductor devices disposed on said heat sinks; acapacitor disposed directly on each of said plurality of heat sinks; anda casing having space and being capable of housing said plurality ofheat sinks; wherein said plurality of heat sinks are arranged withinsaid space of said casing, leaving a clearance therebetween, wherebycontinuous space including said clearance and said passages is formedwithin said space of said casing.
 11. The power module according toclaim 10, wherein said passages of said heat sinks pass an insulativecooling medium.